Compact Plasma and Focused Ion Beams

196 Compact Plasma and Focused Ion Beams

increase in pressure, the height of the peak reduces and the FWHM

broadens due to increase in collisions. In the central region (r = 0–2.5 cm),

the wave propagation is hindered since the plasma is overdense

(. ),.i.e.,> cm for / /GHz74 210 2245

10 3

×==

−

wpwp

p

as shown by the N

i

data, and results in a lower T

e

. Near the periphery (3.2–4.2 cm), T

e

shows an

increase since the plasma density is much below cutoff and wave propaga-

tion can take place through this region [2]. The axial and radial variations of

T

e

and N

i

show similar trends at other powers and pressures.

Axial Wave Field Intensity Measurements